The invention relates to an apparatus at a carding machine, for example but not exclusively, a carding machine having a cylinder which has a cylindrical, clothed wall surface and at least two radial cylinder ends, and having at least one clothed and/or unclothed machine element located opposite the cylinder clothing at a spacing therefrom and two stationary side screens, on which there are mounted holding devices for work elements, for example sliding bends, stationary carding elements, cylinder coverings, which in use are subjected to heat.
The effective spacing of the tips of a clothing from a machine element located opposite the clothing is called a carding nip. The said machine element can also have a clothing but could, instead, be formed by an encasing segment having a guide surface. The carding nip is decisive for the carding quality. The size (width) of the carding nip is a fundamental machine parameter, which influences both the technology (the fibre processing) and also the running characteristics of the machine. The carding nip is set as narrow as is possible (it is measured in tenths of a millimeter) without running the risk of a “collision” between the work elements. In order to ensure that the fibres are processed evenly, the nip must be as uniform as possible over the entire working width of the machine.
The carding nip is especially influenced, on the one hand, by the machine settings and, on the other hand, by the condition of the clothing. The most important carding nip in a carding machine having a revolving card top is located in the main carding zone, that is to say between the cylinder and the revolving card top unit. At least one of the clothings bounding the work spacing is in motion, usually both. In order to increase the production of the carding machine, endeavours are made to make the speed of rotation or velocity of the moving elements, in use, as high as fibre processing technology will allow. The work spacing changes as a function of the operational conditions, the change occurring in the radial direction (starting from the axis of rotation) of the cylinder.
In carding, larger amounts of fibre material are increasingly being processed per unit time, which results in higher speeds for the work elements and higher installed capacities. Increasing fibre material throughflow (production) leads to increased generation of heat as a result of the mechanical work, even when the work surface remains constant. At the same time, however, the technological result of carding (web uniformity, degree of cleaning, reduction of neps etc.) is being continually improved, leading to more work surfaces in carding engagement and to closer settings of those work surfaces with respect to the cylinder (drum). The proportion of synthetic fibres being processed is continually increasing, with more heat, compared with cotton, being produced as a result of friction from contact with the work surfaces of the machine. The work elements of high-performance carding machines today are fully enclosed on all sides in order to meet the high safety standards, to prevent emission of particles into the spinning room environment and to minimise the maintenance requirement of the machines. Gratings or even open material-guiding surfaces, which allow an exchange of air, belong to the past. As a result of the circumstances mentioned, there is a marked increase in the input of heat into the machine whereas there is a marked decrease in the heat removed by means of convection. The resulting increase in the heating of high-performance carding machines results in greater thermoelastic deformations, which, because of the unequal temperature field distribution, influence the set spacings of the work surfaces: the spacings between the cylinder and the card top, doffer, fixed card tops and separating-off locations decrease. In extreme cases, the nip set between the work surfaces can be completely used up as a result of thermal expansion so that components in relative motion collide, causing major damage to the high-performance carding machine concerned. Additionally, it is especially possible for the generation of heat in the work region of the carding machine to result in different thermal expansions when the temperature differences between the components are too large.
In a known apparatus (EP 0 446 796 A), all parts influencing the work spacing (for example, the cylinder and the card top bars) are preferably fabricated from a material having a high elasticity modulus in order to reduce sagging over the working width. Such a material is, for example, steel or fibre-reinforced plastics material. The material selected has to ensure the desired dimensional accuracy of the part (in the case of the manufacturing procedure in question) and has to be able to maintain that in use. The material should accordingly exhibit less thermal expansion and/or greater thermal conductivity so that heat losses which occur (which are unavoidable at high production rates) do not result in disruptive deformation of the work elements. In the case of the known apparatus, the thermal expansion of the co-operating components influencing the work spacing, namely that of the cylinder (drum) and of the card top bars, is equal and homogeneous, because the components are made of the same material. Even though the material should exhibit less thermal expansion, the carding nip is reduced in undesirable manner—albeit to a small extent—which results in problems ranging from reduced carding quality to disruptions in operation. In addition, it is disadvantageous that widening of the cylinder as a result of centrifugal force cannot be reduced or avoided by the known measures.
It is an aim of the invention to provide an apparatus of the kind mentioned at the beginning that avoids or mitigates the mentioned disadvantages and that especially makes possible a carding nip or work spacing, between the cylinder clothing and the clothed and/or not clothed counterpart element, that remains constant or virtually constant when heat is generated.